Studies in this laboratory are designed to elucidate the role of DNA repair processes in human diseases and in carcinogenesis and in normal and abnormal aging. Most studies have been conducted with cells from patients with xeroderma pigmentosum (XP) who have defective DNA repair plus multiple cutaneous malignancies, and premature aging of sun-exposed skin and of the nervous system. Cells from patients with ataxia telanglectasia, diseases with abnormal cell growth and differentiation, Alzheimer disease, Parkinson disease, Huntington disease, Duchenne muscular dystrophy, retinitis pigmentosa, and Cockayne syndrome and from patients with the following primary neuronal, muscular and retinal degenerations are also being studied. These studies are designed to elucidate the pathogenesis of these disorders. We assess the bilogical effectiveness of DNA repair primarily by in vitro assays of cell after treatment of the cells with the DNA damaging agents.